How can I tell if this guy is just being a flirt or if he is seriously interested in me?

ok so there is this guy I know and we both do the same sport and go to the same school so we practice together all the time and he is a huge flirt....
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ok so there is this guy I know and we both do the same sport and go to the same school so we practice together all the time and he is a huge flirt. but people have been telling me that he is totally flirting with me like he has an attraction to me. but I can't tell so I need advice on how to tell fo sure if a guy is interested in you or not.

but to help you out with the advice I will tell you how a normal practice goes. we are both divers. like normal we take our turns doing our tricks off the diving board and he always tell me how good I am. he made up a nickname for me and always says "you got this______" or "goodluck ______" (insert nickname) he always asks for advice from me on how to do something. and the other thing is that he sometimes can't look me straigt in the eyes. what do you think?